title: Retinal nerve fiber layer thickness and cognitive ability in older people: the Lothian Birth Cohort 1936 study.
abstract: BACKGROUND
  This study aims to examine the relationship between the retinal nerve fiber layer (RNFL) thickness as measured by optical coherence tomography (OCT) and lifetime cognitive change in healthy older people.
  
  
  METHODS
  In a narrow-age sample population from the Lothian Birth Cohort 1936 who were all aged approximately 72 years when tested, participants underwent RNFL measurements using OCT. General linear modeling was used to calculate the effect of RNFL thickness on three domains; general cognitive ability (g-factor), general processing speed (g-speed) and general memory ability (g-memory) using age at time of assessment and gender as co-variates.
  
  
  RESULTS
  Of 105 participants, 96 completed OCT scans that were of suitable quality for assessment were analyzed. Using age and gender as covariates, we found only one significant association, between the inferior area RNFL thickness and g-speed (p = 0.049, η2 = 0.045). Interestingly, when we included age 11 IQ as a covariate in addition to age and gender, there were several statistically significant associations (p = 0.029 to 0.048, η2 = 0.00 to 0.059) in a negative direction; decreasing scores on measures of g-factor and g-speed were associated with increasing RNFL thickness (r = -0.229 to -0.243, p < 0.05). No significant associations were found between RNFL thickness and g-memory ability. When we considered the number of years of education as a covariate, we found no significant associations between the RNFL thickness and cognitive scores.
  
  
  CONCLUSIONS
  In a community dwelling cohort of healthy older people, increased RNFL thickness appeared to be associated with lower general processing speed and lower general cognitive ability when age 11 IQ scores were included as a covariate.
authors.affiliation: Princess Alexandra Eye Pavilion, NHS Lothian, Scotland, UK. draugustinuslaude@gmail.com
authors.forename: Augustinus
authors.initials: A
authors.lastname: Laude
authors.forename: Gerassimos
authors.initials: G
authors.lastname: Lascaratos
authors.forename: Ross D
authors.initials: RD
authors.lastname: Henderson
authors.forename: John M
authors.initials: JM
authors.lastname: Starr
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Deary
authors.forename: Baljean
authors.initials: B
authors.lastname: Dhillon
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D003071:Cognition / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology; D016014:Linear Models; D008297:Male; D009898:Optic Disk / Q000033:anatomy & histology*; D012165:Retinal Ganglion Cells / Q000166:cytology*; D012606:Scotland; D041623:Tomography, Optical Coherence